Spinal stabilization and spinal fusion are procedures that involve joining two or more adjacent vertebrae with a bone fixation device to restrict movement of the vertebra with respect to one another. Spinal fixation devices can be used to perform spinal stabilization or spinal fusion. In particular, spinal fixation devices are used in spine surgery to align, stabilize or fix a desired relationship between adjacent vertebral bodies. Such devices typically include a spinal fixation member, such as a relatively rigid fixation rod, a dynamic or flexible spinal rod, or a suitable a longitudinal rod, that is coupled to adjacent vertebrae by attaching the spinal fixation member to various bone anchor, such as, hooks, bolts, wires, and screws. The bone anchor may commonly include heads with channels in which the longitudinal rod is inserted and subsequently clamped by a set screw or closure cap. Surgeons may commonly choose to install multiple bone anchors, as well as multiple spinal fixation members, to treat a given spinal disorder. The spinal fixation member may have a predetermined contour, and once installed, the longitudinal rod may hold the vertebrae in a desired spatial relationship, either until desired healing or spinal fusion has taken place, or for some longer period of time.
The process of positioning and setting the vertebrae may involve adjusting the angular orientation of the bone anchors relative to the spinal stabilization member along the sagittal plane in order to angularly correct the spine. (i.e., sagittal angular correction). The sagittal angular correction of the spine can be performed, for example, to correct kyphosis. In some conventional spinal stabilization systems, the sagittal angular correction of the spine is achieved by adjusting the position of the patient. In some others, it is done via an open surgery which includes a long incision which can result in long recovery times.